JP2002543560A - Device and method for introducing hydrogen into flat display - Google Patents

Abstract

(57) Abstract: A device for introducing hydrogen into a field emission or plasma addressed liquid crystal type flat display (14) has been described, which comprises a wall capable of transmitting hydrogen gas as a function of temperature (13). ) Is formed from a storage section (11) containing a hydrogen storage material (21). The device includes a heater (19) and a heater (22) to bring the wall and occlusion material to a desired temperature, respectively, or one heater that performs two functions. In addition, it describes how the device is activated whenever the flat display is activated, the switch-on of the heater being arranged to bring the wall itself to a pre-calculated temperature.

Description

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a device and a method for introducing hydrogen into a flat display.

In particular, the invention relates to a field emission display (“Field Emission”).
For devices and methods for introducing hydrogen into liquid crystal displays, commonly known as "Displays" or FEDs) and liquid crystal displays, the orientation of the liquid crystal is controlled by a plasma ("plasma addressed liquid crystal"("Plas
ma. Addressed Liquid Crystal ") displays, or PALCs, commonly known in the art), which maintain these hydrogen partial pressures within desired values. The primary use of these types of displays is relatively heavy Thus, it is an alternative to conventional television screens based on the location of a cathode ray tube, especially in the case of PALC, another application is a board for providing traffic information at railway stations or airports.

[0003] In principle, the internal space of the FED should be kept in a vacuum, and that of a PALC plasma chamber is only the noble gases required for plasma formation, typically about 50-500.
Should contain helium, at a pressure of mbar. However, both devices
It is known that if small amounts of hydrogen are present within them, they work better and especially retain their functionality for a longer time.

[0004] "IEEE Transactions on Electron Devi
ces ", Vol. 38, No. 10 (1991), pages 2355-2363.
Et al., And "Vacuum", Vol. 45, No. 2-3 (1994), pp. 235-239.
In FEDs, hydrogen is a metal
It has the function of preventing oxidation of electron-emitting microchips; the optimal hydrogen pressure is about 10 ^-Five ~ 2 × 10^-1mbar.

In PALC, hydrogen causes helium plasma by accelerating the return of a single spot (referred to as a “pixel”) that forms a display from “switched on” to “switched off”. Decay time (dec
It has the function of accelerating its time; a high rate of change of this
This is necessary for transmission of television images of high definition. Patent application EP 816898 describes in detail the mechanism and problems of PALC operation; hydrogen partial pressures of about 0.1-100 mbar, preferably 1-10 mbar, are optimal for PALC operation.

[0006] The introduction of a desired amount of hydrogen into these devices can be difficult during manufacture, for example, by FE.
After evacuation of the interior space of D or the plasma chamber in the case of PALC, it can be carried out by filling with hydrogen gas; this filling operation is performed using the same tubing (usually glass) used for evacuation. Can be implemented, which can later be sealed by heat compression (a method known as "tip-off").

However, hydrogen is consumed during the lifetime of these displays. In particular,
It has been observed that the hydrogen consumption rate is negligible when the display is off, while it is negligible when the display is off. The reason for this behavior is believed to be due to the ionization of hydrogen, because when the display is switched on, H ⁺ ions are generated by electron beam interaction in FED and by plasma generation in PALC; The H ⁺ ions thus generated are accelerated by the electric field and, along with the switched-on display, are present towards the internal parts thereof, mainly the metal microchips of the FED or the electrodes of the PALC, and these parts Absorbed.

[0008] Therefore, it is necessary to provide for the possibility of supplying gas to the internal space of the display when needed and for the life of these displays. Systems devised so far for this purpose are based on the use of hydrogen storage materials, usually zirconium or titanium-based alloys, which can absorb and release hydrogen according to the equilibrium conditions that are characteristic of each alloy. These alloys are simultaneously "exposed" to hydrogen at a pressure of about 10 < ^-4 > to 2 bar and heated to a temperature of about 50 to 200 [deg.] C. with hydrogen in an amount up to a few percent of their mass. (“Charged”). Occluded hydrogen can then be released from the alloy when the hydrogen partial pressure is reduced below the equilibrium partial pressure for a particular alloy at a particular temperature. The type of alloy that stores hydrogen may be located inside the display in communication with the interior space, and a temperature of about 40-500 ° C. when the hydrogen partial pressure drops at a value greater than indicated for FED and PALC. To re-fix the optimal working atmosphere in the device. The use of zirconium or titanium alloys based on hydrogen storage and release equilibrium properties,
For example, patent applications EP716772 and EP
838832 and JP-A-10-199454, and patent applications EP-816898, EP83363 and WO98 / 57 concerning PALC type displays.
219.

Prior art systems are, in principle, effective at retaining hydrogen at desirable levels, but are difficult to implement. This is because it is difficult to define a particular alloy having a hydrogen equilibrium pressure as a function of the temperature at which the desired hydrogen pressure can be generated inside the display. In particular, a major difficulty encountered with these systems is that these alloys typically have very low hydrogen equilibrium pressures near room temperature (operating temperatures of FED and PALC), and as a result, Most of the hydrogen released by heating is immediately reabsorbed by the alloy itself when cooled;
At temperatures near room temperature, the alloy acts as a hydrogen getter rather than a source of hydrogen.
This is because the alloy can also absorb hydrogen intentionally supplied to the display during the manufacturing stage.

[0010] In patent application MI99-000534, the Applicant proposes to introduce hydrogen into a flat device based on the use of a portion of the passage wall between the hydrogen supply and the flat display formed of a proton conductor material. Tried to provide devices and methods. The flow of hydrogen gas through the wall is controlled by two electrodes, and a first electrode is connected to the surface of the proton conductor material facing the interior of the reservoir and a second electrode is connected to the surface facing the interior space of the display. Is done. Further, the method monitors the display continuously as the hydrogen partial pressure falls below a predetermined critical value to allow the application of an appropriate potential difference between the two electrodes. , Or at least involves detecting it.

It is an object of the present invention to provide a device and method for introducing hydrogen into a flat display, which controls the potential difference applied to the electrodes connected to the two surfaces of the proton conductor material, in a desirable sense. It provides a self-regulating system without the need for a possible pressure sensor and without external intervention. This object is achieved by the present invention using a device according to claim 1 and a method according to claim 7.

[0012] These and other objects, advantages and features of the devices and methods will become more apparent from the following detailed description, which is given for a number of different embodiments in conjunction with the drawings. The device according to the invention consists of a reservoir containing a material capable of occluding and releasing hydrogen as a function of temperature; the walls of the reservoir are impervious to hydrogen.
a material that is permeable to hydrogen as a function of temperature, preferably palladium or an alloy thereof or iron or an alloy thereof; Connects to the storage in the internal space. The flow F of hydrogen gas that can permeate the membrane is given by the well-known equation:

[0013]

(Equation 1)

Where A is the area of the film, d is its thickness, and ko and Ek are each
Pre-exponential factor and activation energy, which depend on the material forming the film
And then P₁ And P_Two Is the value of the hydrogen pressure on the surface facing the membrane. P_Two so
, The pressure value on the side of the reservoir, and P₁ Defines the pressure value on the side of the display.
And the flow is P_Two > P₁ At the time, the storage is directed to the display, _Two <P₁ Is opposite direction when; P_Two = P₁ When the equilibrium is reached and the net through the membrane
Does not flow. Irrespective of the direction of flow, the velocity increases with the temperature of the membrane.

Referring to the drawings, in FIG. 1, the device of the invention is shown schematically and in a general manner. The device 10 consists of a reservoir 11 demarcated by a collection of walls, usually shown as a membrane 12. The device comprises a wall (or part thereof) formed by a membrane 15 of a material 16 permeable to hydrogen gas as a function of temperature.
Thus, it is connected to the internal space of the flat display 14 of the FED or PALC type, and has a surface 17 facing the storage unit 11 and a surface 18 facing the space 13. Around the membrane 15 or in any way contacting it is provided a heater 19 of any type, suitable for checking the temperature of the membrane 15, for example an externally supplied electrical resistor , But only a few shapes are schematically shown in part in the figures. The material 21 capable of absorbing and releasing hydrogen by heating is provided in the storage unit 11;
buffer, which may be one of the titanium- or zirconium-based alloys described in the above-mentioned known documents, particularly ZrCo, ZrNi, ZrCo _{1- x} Ni _x , or a ternary Zr-V-Fe alloy, And LaNi ₅ or LaN
i _5-x Al _x . The material is preferably such that, at a temperature Ti easily achievable in the device, its equilibrium hydrogen pressure is maintained in the space 13 of the display and can already be introduced into the space during the manufacturing stage. , it is chosen equal to hydrogen pressure value P _s. Temperatures T ₁ is the normal comprised between room temperature and about 400 ° C.; From this low temperature, usually, the assembly, is not easy use, and requires a cooling system of the device, whereas higher temperatures it Requires a relatively large amount of power to achieve, and can damage the device itself. Normally, the material 21, the equilibrium pressure is selected to a temperature equal to P _s is about 150 to 300 ° C.. Heating member is storage unit 11
Can be provided for the heating material 21, such as a resistor 22 disposed directly inside the connector, and can be provided by a connector 23 as shown or outside thereof.

As mentioned above, hydrogen with pressure P _s (full for FED and partially for PALC) is introduced inside the space 13 during the manufacturing stage of the display 14.
During the lifetime of the display, hydrogen is consumed and its pressure is reduced to a value of P _x <P _s . In order to re-establish the desired pressure in the display, the material 21 is brought to the temperature T ₁ by the heater 22, the reservoir pressure reaches the value P _s , and according to equation (I), from the reservoir to the space 13. flow is ensured, the pressure in the space reaches again the desired value P _s, and stops. The arrival of the condition can be detected by a suitable sensor located in the space 13, but to simplify the assembly of the display, ensure that the device 10 is always heated when the display is on. It is preferred, as a result, pressure is self-adjusting to the continuous value P _s. It is possible to influence the film temperature by keeping it as high as possible at the value T ₂ to facilitate the transport of hydrogen; however, this value avoids damaging other requirements of the display. Therefore, it cannot rise above about 400 ° C. For the same purpose,
It is also preferable to use a film having a thickness as small as possible.

When the display is off, especially to save energy, the device 1
Preferably, no zero is also supplied. Under these conditions, the display and
All elements of device 10, in which material 21 is brought to room temperature and the display is
When used in traffic signals or other environments, it can fluctuate in the range of about 0-50 ° C.
sell. At these temperatures, material 21 typically has a very low equilibrium pressure,
As a result, according to equation (I), the flow is directed toward the reservoir and the device 10
It tends to absorb substantially all hydrogen present. Therefore, the film 15 has T _a It is necessary to have the smallest possible transmission value at the same time. In this case, the temperature is
Since it is constant, the control of the flow must be as large as possible
Can only be implemented by

[0018] Thus, the thickness d of the membrane 15, the temperature has a good permeability when the T _2, whereas that the temperature is considering conflicting requirements of having a reduced permeability when T _a Is determined by To determine the thickness d, it is convenient to refer to the curve shown in the graph of FIG. 2, which passes through palladium membranes having different thicknesses as a function of the membrane temperature T expressed in ° C. The flow F (expressed in mbar · l / s) is shown; the curves in FIG.
. Means membranes 25 mm, 0.5 mm and 1 mm thick, effective for membranes having an area of 0.25 cm ² and when the hydrogen pressure difference ΔP = P ₂ −P ₁ between the two membrane surfaces is 5 mbar. is there. The value of the membrane area is typical of a typical use in a display, where the surface of the interior space 13 is mainly occupied by its operating elements, and the area available for the membrane is reduced. A value of 5 mbar for ΔP is instead chosen as representative of the worst conditions that can occur in a PALC-type display, given that 5 mbar is the hydrogen partial pressure value to be maintained inside the PALC-type display. During the operation of the display operation under worst-case conditions, the space 13 is sufficiently exhausted of hydrogen, so that the previously defined values P _s and P _x are 5 and 0 mb respectively.
equals ars, is [Delta] P = 5 mbar; display is off, when it is T = T _a, the inside of the hydrogen pressure reservoir 11 may approach the 0mbar, while the partial pressure of the space 13 is not higher than 5 mbar So a pressure difference of 5 mbar at the two membrane surfaces is again obtained (
Although it is the opposite sign to the above). In the worst case, T ₂ is known at _Ta = 50 ° C. (defined by the display manufacturer as the highest temperature experienced by the membrane 15).
Then, from the curves in FIG. 2, it is possible to select a membrane pressure that meets all the conditions found in the device 10 and the display 14. A similar curve as shown in FIG. 2 can be obtained for a desired application is FED, for membranes of materials other than palladium, for ΔP values of less than 5 mbar, for example about 10 ⁻¹ mbar.

During operation of the device 10, it can be expected that the temperatures T ₁ and T ₂ of the material 21 and the film 15, respectively, are different, but the assembly and operation of the device is subject to the condition T _i = T _2. This condition is greatly simplified when
And 22 can be achieved by employing only one heater. This situation is chosen by the manufacturer, but imposes further restrictions on the choice of the thickness d of the membrane 15. This is because, in this case, the temperature cannot be chosen as high as desired within the limits given above, in order to avoid too high a hydrogen equilibrium pressure in the reservoir 11. In particular, a pressure higher than P _s overloads the space 13 with gas.

The use of the device according to the invention is furthermore advantageous from the point of view of the compatibility required for the flat display manufacturing process. In fact, the storage material (buffer) should already have stored hydrogen at the required concentration before mounting on the device. The thermal cycling experienced by the assembly during the manufacturing process can result in higher temperatures than the device in operation, resulting in gas loss due to hydrogen release from the storage material and pumping of the gas during the manufacturing phase. By conventional methods system storage material is in direct contact with the display internal space, in order to minimize and H ₂ losses, at 450 ° C., or after the frit sealing operation performed by keeping cooled during this phase,
Although it is necessary to place the storage material, both of these solutions involve the same difficulties. The device according to the invention, for example based on ZrCo, can easily withstand heating up to 300 ° C. during the pumping for 150 minutes on the other side and the hydrogen loss is limited to about 3 mbar · l. This is an absolutely acceptable value for the total amount of hydrogen contained on the order of about 80 (mbar · l) / g in the material.

Examples of membrane thickness dimensions and operation of the device of the present invention are described below. Example 1 In this example, reference is made to the numbering of FIG. Internal capacity 150cc
A display of the PALC type having the following is connected to the hydrogen releasing device of the present invention, which comprises 1 g of the ZrCo compound pre-stored with 8 mg of hydrogen by a known method,
It is mainly formed from a reservoir with steel walls. The interior and storage of the PALC are
^They are connected to each other by a palladium membrane having a surface of 25 cm ² . Membrane and
One resistor is used to heat the compound ZrCo through the reservoir wall,
As a result, under operating conditions, the compound and the membrane are at the same temperature. PALC is charged by glass tubing with a helium / hydrogen mixture having a total pressure of 150 mbar, where hydrogen is present at a partial pressure of 5 mbar as shown in FIG. The tubing used to charge the gas mixture is connected to a gas sampling system, which in turn is connected to a mass spectrometer for measuring the gas chemical composition contained in the PALC by means of an expansion chamber. ing. The thickness of the membrane is determined by comparing the following conditions reported by the PALC manufacturer with the curves in FIG. That is, when the display is on, the hydrogen consumption is about 3 × 10 ⁻⁷ (mbar · l) / s, and when the display is off, the maximum acceptable hydrogen loss is 100 ° C. at 50 ° C.
About 1 mbar per day, which is about 6 × 10 ⁻⁸ (mbar · l) / s of the device described above.
Equal to the transmission flow; this value of removal flow F _r is shown in the figure by a first dotted line. When the display is on, it is a hydrogen flow into the space 13 is equal at least to hydrogen consumption rate of the above, preferably 1 it is requested order of magnitude larger; in this case ^{3 × 10 -6 (mbar · l} ) / s suitable flow value F _H is is illustrated by the second dashed line. The material ZrCo is in equilibrium at about 180 ° C. at a hydrogen pressure of 5 mbar, and according to a preferred embodiment of the invention, the temperature is also imposed on the membrane 15. The film is 6 × 10 ^-8 (mb
ar · l) / s, and 3 × 10 ⁻⁶ (mbar · l) / s at 180 ° C.
Conditions with higher permeation flow limit a film thickness of 0.35 mm. The membrane 15 and the material ZrCo are heated to 180 ° C., the display is switched on,
Left to run for several hours: the hydrogen partial pressure contained in the screen is 0.5 cc
It is measured hourly by withdrawing with a tubed gas sample having a volume of and analyzing them with a mass spectrometer. The variation trend of the hydrogen partial pressure so measured (expressed in mbars) over time (hourly) is shown as curve 5 in FIG.
Example 2 (Comparative) The test of Example 1 is repeated for PALC, but the hydrogen release device of the present invention is not coupled to it. The trend of hydrogen partial pressure over time is shown as curve 6 in FIG.

As is evident from the comparison of curves 5 and 6 in FIG. 3, the device and the method according to the invention keep the hydrogen partial pressure essentially constant except for small fluctuations in the PALC, On the other hand, in PALC without the device, the hydrogen partial pressure decreases by 14% of the initial value in the first 100 durable times. Thus, the devices and methods of the present invention may provide sufficient buffer material and membrane heaters to obtain sufficient self-regulation of the hydrogen partial pressure in a flat display without the required external control.

[Brief description of the drawings]

FIG. 1 schematically shows one embodiment of the device according to the invention.

FIG. 2 shows the flow of hydrogen gas through the permeable palladium wall of the device according to the invention.
4 shows a graph plotted against wall temperature for four different thickness values.

FIG. 3 is a graph showing the tendency of hydrogen partial pressure to fluctuate in a flat display provided with the device of the present invention and a flat display not provided with the device.

Claims (11)

[Claims] A reservoir (11) containing a material (21) capable of releasing hydrogen, the walls (12) of which are made of a material impervious to hydrogen, but the part (15) has a function as a function of temperature; One surface (17) permeable to hydrogen gas and facing the reservoir (11)
And an opposite surface facing the interior space (13) of the flat display,
Introducing hydrogen into the flat display (14) comprising: a reservoir (11); and means (19) for heating said part (15) comprising a material permeable to hydrogen as a function of temperature. Devices (10
). 2. The device according to claim 1, wherein the wall of the reservoir is made of metal, ceramic or glass. 3. The device according to claim 1, wherein the material permeable to hydrogen as a function of temperature is selected from palladium and its alloys or iron and its alloys. 4. The device according to claim 1, wherein said hydrogen releasing material is selected from zirconium-, titanium- or lanthanum-based alloys. 5. The method according to claim 1, wherein the hydrogen releasing material (21) is ZrCo, ZrNi, ZrCo. _1-x Ni_x 5. The device according to claim 4, wherein the device is selected from a ternary alloy of Zr-V-Fe.
chair. 6. The hydrogen releasing material (21) is made of LaNi._Five And alloy LaNi _5-x Al_x 5. The device of claim 4, wherein the device is selected from: 7. The flat display according to claim 1, further comprising the step of heating at least a portion located between the reservoir and the interior space of the flat display and permeable to hydrogen as a function of temperature. A method of introducing hydrogen. 8. The method of claim 7, wherein the hydrogen releasing material is also heated. 9. The method according to claim 7, wherein the permeable wall portion and the hydrogen releasing material are both heated to the same temperature T. 10. The method according to claim 7, wherein the portion made of a material permeable to hydrogen is heated at a temperature higher than the heating temperature of the hydrogen releasing material. 11. The operation of the flat disc plate includes heating at least the portion made of a material permeable to hydrogen to coincide with the simultaneous operation of the device.
The described method.